Network switches, routers and other devices that forward packets in a network can be forced to delay the forwarding of packets in a given packet flow when a downstream switch or other destination device becomes unable to accept new packets in that flow. In some applications, packet flows are assigned to classes of service that the switch or packet processor needs to honor. However, within one class of service, some flows may affect the quality of service for other like flows. Since the assignment of packets for a flow to queues is performed at the input port of the switch, the enqueuing process is unaware of a scenario where one flow within a class is degrading the quality of service of other flows. In some cases, this degradation may result in a violation of a service agreement and cause application level issues. The foregoing situation is also known as the head of line (HOL) blocking problem.